In the Old Canyon vs. Young Canyon debate in late 2012, the Old Canyoneers had just put forth a
new paper in the journal
Science declaring the Grand Canyon to be roughly 70 million years old, having been excised
by rivers other than the Colorado.

That figure, if accurate, would make the Grand Canyon so old that dinosaurs could have been the
first tourists.

But another rebuttal was published online yesterday in the journal
Nature Geoscience, stating that the canyon is 5 million to 6 million years old, with some
older stretches, including one patch that reaches almost back to the dinosaur era.

“The canyon we see today is young, but it made use of some old segments,” said Karl Karlstrom,
professor of geology at the University of New Mexico and lead author of the paper.

He added, “The question is resolved that the canyon is not 70 million years old.”

Not so fast.

Brian Wernicke, a California Institute of Technology geologist who co-authored the 2012 paper,
said he still thinks the westernmost stretch of the canyon is 70 million years old.

Both camps rely on thermochronology, which measures the past temperatures of rocks along the
canyon wall. Crystals in the rocks record the decay of radioactive elements into helium as hot,
buried rocks are exposed to the surface by erosion and cool-down.

But there’s another new wrinkle: James Sears, a professor of geology at the University of
Montana, has published research arguing that the myster-

ious river that carved the eastern Grand Canyon about 25 million years ago could have flowed
through Nevada, Idaho and Montana and up through Canada to the Atlantic Ocean.

He bases this on gravel deposits found in Montana that don’t match any of the local bedrock but
do match the bedrock in Nevada.

“The moral of the story is that the tectonics of western North America have been very active in
the recent geologic past, and the way we see it today was not the way it was,” Sears said.